Telephone system



C. WHITE.

TELEPHONE SYSTEM.

APPLICATION FILED MAY 8, 19I8.

1 3 52, 5 68 Patented Sept. '14, 1920.

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, UNITED STATES P TENT OFFICE.

CHARLES WHITE, 0.! EAST'ORANGE, ,NEW JERSEY, ASSIGNOR To WESTERN ELECTRIC COMPANY, INCORPORATED, OENEW YORK, N. Y., A CORPORATION OF NEW YORK TEL PHONE SYSTEM.

sp eeification of Letters Patent. Pat t d S bt 14 2 Application filed May 8, 1918. Serial N 233,259.

To all whom it may concern:

Be itknown that 1, C ARL S WHITE, a citizen of the United States, residing at East Orange, in the county of Essex,State of New Jersey, have invented certaininew and useful Improvements in Telephone Systems, of which the following is a full,-clear, concise, and exact description.

This invention relates to telephone systems and more particularly to systems ofthe central energy type in which a distinctive tone is employed to give an audible signal in the operators receiver on testing a telephone line to indicate theidle or busy condition of that line. r

In telephone systems in whichpolystation lines form a part, it often occurs that one subscriber on a particular polystation line desires to be connected with another subscriber on the same polystation line, Inasmuch as the jacks of all the stations on that line would test busy when the answering operator inserts the answering end of a cord circuit into the ack of the calling party, it has been found necessary to give a different signal to distinguish between this condition and the condition existing when a call is extended to another busy line. Testing arrangements of this character are known in the art as reverting busy tests. While various reverting busy test arrangements have been suggested, the range of permissible variations from ideal conditions hasv been somewhat limited, requiring close adjustment and careful supervision 'of the apparatus involved and the object of the pres ent invention is to provide an improved reverting busy test system of increased eflicienc'y capable of operation, .over a wide range of operating conditions.

In accordance with afeature of the invention, there is provided a cord circuit of the usual type with which there is associated a busy test relay for controlling the connection of a source of tone supply with a test conductor of the cord circuit and in addition there is provlded a resistance COll which is adapted to be connected in parallel relation with the test conductor of the cord circuit upon the actuation ofthe listening key to effect the operation of the busy test relay;-

In the accompanying drawing, a telephone system is diagrammatically shown which illustrates one embodiment of the in vention.

For the purpose of illustrating the inventlon, assume that subscriber A desires to converse with subscriber B whose station is onthe same line as that of subscriber A. A

would initiate the call by removing the re-;

ceiver' at his station from its switchhook, thereby causing the operation of line relay 4 wh ch 111 turn completes the circuit for line lamp 5. The operator, upon observing the lighted condition of line lamp 5, inserts the answer-mg plug 6 of the cord circuit G into Jack 7, whereupon cutoff relay 8 is operated over a circuit extending from battery through the supervisory lamp 10, normal contact of relay 9, sleeve contacts of the plug 6 and thejack 7, andwinding of cutoff relay 8 to ground. The operation of this relay causes the release of line relay 4 which in turncauses the eflacement of line lamp 5. Supervisory relay 9 is also operated an instant later over a circuit extending from battery through winding 32 of the repeating coil 11, winding of supervisory relay 9, ring contacts of the plug 6 andthe jack 7, substation apparatus of station A, tip contacts of the ack 7 and plug 6, and winding 33 of repeating coil 11 to ground. The operation of relay 9 opens at its normal contact the low resistance path extending in parallel about resistance 21 and connects at its alternate the resistance in the circuit previously traced for the cutoff relay 8 is increased due to the opening of the parallel path about resistance 21, the two batteries just mentioned act in a parallel aiding relation as regards current passing through the resistance 21 and thus supply sufiicient current to relay 8 to maintain it in actuated position} The operator would now actuate listening key 12 which connects the operators telephone set 13 to the talking strands of the cord circuit, thereby permitting theoperator to ascertain the number of the called-for party. The actuation of key 12 also prepares a circuit for the tone supply 14, which is adapted to be connected to the sleeve conductorof plug 6 through contact 15 of this key. The resistance 20 is at the same time connected'in parallel relation with the sleeve conductor of the .cord circuit and is provided for the purpose of reducing the ef- 't'ective resistance therein as will ap more clearly from the Iollowing dest iption. A circuit for a busy test relay 16, preferably common to a plurality oi cord circuits, is also established through contact 17 of listening key 12 on actuation therco'l.

On ascertaining that subscriber A desires to be connected with subscriber B, the operator would touch the tip of the calling plug 18 to the sleeve contact of ack 19 which is individual to station B, in order to determine whether or not the line is idle or busy. In the case of polystation lines, each. subscriber has an individual answering jack, the numbers of which are in many cases radically different from the numbers of other subscribers on the same line, so that the number called does not in itself indicate to the operator whether the called-for party is on the same line as that oi the calling party or not. In order to determine this fact, it is necessary to test the line as above indicated. lVhen the connection has been completed between the tip of plug 18 and the sleeve of jack 19, relay 16 is operated over a circuit extending from battery through the alternate contact of supervisory I relay 9, resistance 21, sleeve contacts of the plug 6, jacks '7 and 19, tip contact of plug contact 17 of key 12, and the winding o't busy test relay 16 to ground. The operation of relay 16 thereby connects a source of tone supply 1% with the test conductoi, produc ing a click in the operators receiver, followed by a tone which indicates whether or not the called-for party is on the same line as the calling party. In systems as herein represented, the operation relay i6 is assured as the shunting effect of winding 31 of repeating coil 11 which is connected in parallel relation with the winding oi? busy test relay 16 is thereby minimized. The resistance of winding 31 of repeating coil 11 is preferably much lower than that of the winding of relay 16, therefore, the current flow through the latter is in many cases not of a suflicient strength to cause its operation since a large amount of the total current flows thrugh winding 31 of repeating coil 11. Resistance 20 which is connected in parallel with resistance 21 through contac 15 of the listening key thereby reduces the effective resistance of the sleeve conductor,

so that the current strength is increased to such anamount that the busy test relay 16 receives an amount of current sutiicient to from the source 14: through the contact of busy test relay 16, contact 15 of listening key 12, sleeve conductor of the cord circuit C, sleeve contacts of the plug 6, acks 7 and 19, tip contact of plug 18, contact 17 or" key 12, induction coil 22 of the operators telephone line.

telephone set 13, receiver 23, condenser 24, contact 25 of key 12, winding of calling supervisory relay 26. winding84c of repeating coilll, and battery to ground. The operator thereupon receives a definite tone signal in her receiver distinctly different from the click of the usual busy test signal and is thereby advised that the called-1'01? party is "on the same line as the calling party. Plug 18 would then be inserted into jack 19 which causes the operation oi supervisory relay 26 to effect the efliacement ct supervisory lamp 27 as before described, and the release of the busy test relay .16 which in turn disconnects the tone supply .14 from the sleeve conductor of the cord circuit. Party B would then. be signaled in any desired manner.

To illustrate the difference in character of the signals received by an operator in testing a busy line other than that of the calling subscriber, assume that subscriber A desires to converse with party-D, who is on another In this case, the operator would engage the tip contact of the calling plug 18 with the sleeve contact of the jack 28 belongingto the line of party D. The

usual busy test click will be produced in the operators receiver it the line tested is busy upon the engagement of the tip con- I but no tone will be produced in the operators receiver, due to the fact that the answering end of the cord circuit is engaged by the jack of another line. However, if the line tested is idle, there will be no click produced in theoperators receiver. The plug 18 may then be inserted into jack 28, causing the operation of cutoff relay 29 which opens the circuit for line relay 80. Supervisory lamp 27 is also illuminated upon the insertion of plug 18 into jack 28. The party D would then be signaled in any desired manner. The called-for subscriber upon the removal of the receiver from the switchhook causes the operation of supervisory relay 26 over a circuit similar to that of relay 9, the operation of which arranges a shunt about the supervisory lamp 27 which causes the eflacement of the same.

hen the conversation has been completed, and the subscribers again restore their receivers to the switchhooks, supervisory relays 9 and 26 are thereupon re leased, which opens the circuit oi the opposing batteries, thereby causing the supervisory lamps 10 and 27 to be illuminated. The operator, upon observing the lighted condition of these lamps, can then remove the plugs from the respective jacks, which restore all apparatus to normal.

What is claimed is:

1. A telephone exchange system comprising a telephone line terminating in a plusistance coil common to a plurality of cord circuits, said resistance coil being connected in parallel relatlon with the third conductor of said cord circuit upon the actuation of said key to effect the operation of said relay.

3. A telephone exchange system comprislng a telephone line terminatlng in a plurality of jacks, a three-conductor cord circuit, the answering end of which is adapted to be associated with one of said jacks, a busy test relay, an operators telephone set including a receiver, a resistance coil, and a listening key for connecting said operators telephone set with the talking conduc-j tors of said cord circuit and to connect said resistance coil in parallel relation with the third conductor of said cord circuit, said busy test relay being operated upon the engagement of the calling end of said cord circuit with the test thimble of another jack of the same line to produce an audible tone in the operators receiver.

4. A tele hone exchange system comprising a telep one line terminating in a plurality of jacks, a three-conductor cord circuit, the third conductor of said cord circuit serving as a test conductor therefor and being adapted to be connected with the'test terminal of one of the jacks to determine the idle or busy condition of the line, a busy test relay, a listening key, and a resistance coil connected in parallel relation with the test conductor upon the actuation of said key to eii ect the operation of said relay.

5. A telephone exchange system comprising a telephone line terminating in a plurality of jacks, a plurality of cord circuits having a test conductor adapted to be connected with atest thimble of a jack to de termine the idle or busy condition of the line, an operators telephone set, a busy test relay, a resistance coil common to said cord circuits, and means for connecting the operators telephone set with the talking conductors ofsaid cord circuit and to connect said resistance coil in parallel relation with the test conductor of said cord circuit to effect the operation of said relay.

6. A telephone exchange system comprising a telephone line terminating in a plurality of jacks, a three-conductor cord circuit, a test relay, a resistance coil common to a plurality of cord circuits, and a listen ing'key adapted when actuated to connect said resistance coil in parallel relation with a conductor of said cord circuit to thereby assure the operation of said relay.

In witness whereof, I hereunto subscribe my name this 2nd day of May A. D., 1918.

CHARLES VVHITEL 

